1. Field of the Invention
The present invention relates to an optical data bus, in particular having a statistical access method, for the transmission of data between transmitters and receivers in the form of clock signals, particularly non-return to zero (NRZ) data, whereby every transmitter has an encoder assigned thereto which encodes the signals to be output from the transmitter onto the data bus in a specific manner and whereby every receiver is preseated by a decoder for decoding the data supplied from the data bus to the receiver and for reacquisition of the clock contained in the encoded data.
2. Description of the Prior Art
A data bus of the type generally set forth above has been proposed by Witte et al in their U.S. Pat. No. 4,491,942, issued Jan. 1, 1985, fully incorporated herein by this reference. A specific example of a statistical or asynchronous access method is the CSMA/CD access method as reported in "Carrier Sense Multiple Access Collision Detection", v. Comm. of the ACM, July 1976, Vol. 19, No. 7, pp. 395-404.
In the proposed data bus, the bit rate on the transmission link is equal to the data bit rate to be transmitted. The encoder assigned to the transmitter is composed of a scrambler which (a) is required for recovering the clock in the receiver and (b) is required for the logical discrimination of the state "do not transmit data" from the state "transmit data". The decoder is composed of an unscrambler. The start of the useful data is to be preceded by so-called header bits and the end of the useful data is marked by end of data mark bits in the form of a defined bit sequence. The clock is recovered, for example by a phase locked loop (PLL) circuit from the bit sequence incoming to a receiver. The receiver controlled is constructed such that the correct clock is reacquired after the header bit sequence and the end of data mark bits and the header bits are separated from the actual useful data.